One step in the process of manufacturing an integrated circuit component is packaging. In packaging, a fabricated semiconductor chip is housed in a protective package. The assembled component can be tested and connected to the electronic circuit for which it was designed. The package is provided with external leads so the component can be electrically connected to the electronic circuit.
A difficult part of the packaging process is connecting the chip to the package's external leads. Care must be taken to insure that each bond or connection point on the chip is properly connected to the appropriate external lead. Failure to make all of the proper connections will result in a malfunctioning or nonfunctioning component.
A current method of connecting the chip to the package leads is Tape Automated Bonding (TAB). TAB employes a polyimide film, having a plurality of individual tape sites. Each site comprises a support ring of film defining a center aperture. A plurality of conductive fingers formed by etching techniques, underlie the support ring. Each conductive finger has an inner lead that extends into the center aperture and an outer lead that extends beyond the outer perimeter of the support ring. A chip is positioned over the aperture so that each bond point on the chip is in registration with the appropriate inner lead. The bond points are then bonded to the inner leads.
The tape-and-chip lead sub-assembly is then excised from the tape. The sub-assembly is positioned on a package substrate so that the outer leads are aligned over appropriate package substrate leads which connect to package external leads of the package. Bonding of the outer leads to the substrate leads then connects the chip to the appropriate package external leads.
More thorough discussions of the Tape Automated Bonding process are set forth in Sze, edit., VLSI Technology, (1983) pp. 559-564, and in Dais, Erich, and Jaffe, "Face-Down TAB for Hybrids," IEEE Transactions on Components, Hybirds and Manufacturing Technology (Dec. 1980) pp. 623-633, which are incorporated herein by reference.
Tape Automated Bonding is an efficient way to connect semiconductor chips to packages. The tape sites can be arranged on the tape to allow for automatic bonding of chips to the tape. By proper etching of the tape, the conductive fingers for each chip can be densely packed at the tape site. This feature is very important in the fabrication of Very Large Scale Integration (VLSI) chips, where often there are 100 to over 300 bonding points per chip.
However, it has proved difficult to align and bond the densely packed tape outer leads to the package substrate leads. There are three reasons for this; (1) curling forces in the leads are different along the tape in-line and across-the-line axes; (2) curling of the metal conductive fingers and the film on which they are etched is different and causes the leads of the sub-assembly to curl; and finally, (3) there is x-y sliding of the individual outer leads when a thermode bonding blade is pushed down on them. This curling and sliding make it difficult to keep the outer leads aligned prior to substrate bonding.
Outer lead curling and sliding also make it difficult to inspect the tape-and-chip sub-assembly prior to lead bonding. To prevent the outer leads from curling out of alignment, it is necessary to promptly bond the outer leads to the substrate leads. Any errors, such as fine misalignment, must be corrected by later inspection and rebonding.
These problems are relatively easy to correct and control when there are 10-100 outer leads per sub-assembly, and there is a lead pitch of more than 0.012 inch. However, VLSI sub-assemblies have 100 or more leads per sub-assembly. The outer leads are densely packed together, i.e., have a finer pitch between leads As a result, it is very difficult to align and bond the tape outer leads of a VLSI TAB sub-assembly to package substrate leads. This has been a major obstacle to the efficient manufacture of VLSI components.
A need, therefore, exists for a new method of bonding the outer leads of the conductive fingers leads of a tape-and-chip sub-assembly to the appropriate substrate leads. The new method should allow for the proper alignment of a large number of outer lead ends to the appropriate substrate leads, regardless of the density of the leads. The method should also prevent the curling of the outer leads prior to their being bonded to the substrate leads. Additionally, it should allow for the intermediate inspection of the sub-assembly after it is aligned on the substrate. This would allow for the correction of misalignment with the leads prior to bonding of the tape leads to the substrate. The new method of bonding should also prevent the outer leads from sliding when a bonding tool is applied to bond a tape outer lead to a substrate lead.